After rebooting (and by every following attempting to start), the phone freezes on the "Unlock device" screen. The keyboard for enetering of unlock code appears, but is not responding. Hardware buttons also don't like to respond. The phone is heating, and after a minute I have to remove the battery because this is the only way to stop it. Soft resets didn't help.

The phone is Samsung Omnia SGH i900, bought in 2008, with the official Samsung ROM last updated in 2009.